LIMB Specific Data Info
The release of significantly improved Intensity-Frequency-Duration (IFD) design rainfall data in 2016 brought opportunity to renew understanding of Australian floodplains, and consequently create safer and stronger communities. However, several councils in SEQLD noted localised nuances in rainfall distribution and severity not reflected by the 2016 IFD data. A suite of new localised IFD data was hence commissioned for four local government areas (LGA), being the Lockyer Valley, Ipswich, Moreton Bay LGAs, and one other area, herein termed the LIMB 2020 IFDs.
The LIMB 2020 IFDs were informed by additional council sub-daily rainfall gauge data, and were developed using methods that placed higher weighting on this data. The method additionally placed enhanced focus on elevation. The developed localised IFDs resulted in a reduction in local biases across all AEPs, durations and areas, compared to the 2016 IFDs.
The LIMB 2020 IFDs come in three formats;
- High resolution; gridded LIMB 2020 IFD output at fine resolution (0.005° )
- BOM resolution; gridded LIMB 2020 IFD output aligned to resolution of BOM 2016 IFDs (0.02479° )
- Envelope of BOM 2016 IFDs / LIMB 2020 IFDs; maximum of the two IFDs (resolution aligned to BOM 2016 IFDs)
The 2020 IFDs were peer reviewed, with the work commended (peer review report is available upon request to the councils). The review supported use of the envelope of the BOM 2016 and LIMB 2020 IFDs.
A paper on the development of the IFDs was presented to the industry at the FMA 2022 Conference in Toowoomba; the conference paper is available at https://www.floods.asn.au/
Australian Rainfall and Runoff 2019 recognised that future techniques and information would be developed subsequent to the publication of the guideline and states that use of new or improved procedures should be encouraged, noting peer review of new processes as a desirable attribute.
Moreton Bay Regional Council formally adopted the LIMB 2020 IFDs in June 2022. Ipswich City Council and Lockyer Valley Regional Council have been progressively incorporating the use of the LIMB 2020 IFDs since the conclusion of the project in June 2021.
Practitioners undertaking works for either Ipswich City Council, Lockyer Valley Regional Council or Moreton Bay Regional Council in general should utilise the Envelope of the BOM 2016 IFDs and LIMB 2020 IFDs. Where project objectives and scope indicate a benefit of utilising the High Resolution LIMB 2020 IFDs (e.g. where spatial variation is particularly sensitive), practitioners working for these councils should contact the relevant council directly to discuss. All other practitioners working within the regions for which 2020 IFDs are available should consider the guidance of Australian Rainfall and Runoff on their use.